Significant inter-individual variability exists in responses of human dorsal hand veins to activation of α-adrenoceptors. Simultaneous graded infusions of the α 1 - and α 2 -adrenoceptor agonists phenylephrine (3.66–8000ng/min) and dexmedetomidine (0.0128–1000ng/min) were given into dorsal veins of both hands and responses of 75 subjects were analyzed to assess whether a subject's sensitivity to phenylephrine (ED 50 ) predicts his sensitivity to dexmedetomidine. Individual ED 50 estimates of dexmedetomidine and phenylephrine ranged between 0.06–412 and 14.2–7450ng/min and exhibited only a weak positive relationship (r 2 =0.074, P=0.018). Finger temperature, body mass index, age and phenylephrine sensitivity together accounted for about 30% of dexmedetomidine ED 50 variation (r 2 =0.315, P<0.001). The large inter-individual variability observed in the responses of dorsal hand veins to both α 1 - and α 2 -adrenoceptor agonists is not explained by some common factors; instead, dorsal hand vein responsivity is separately determined for both receptor mechanisms.